June 13th Wednesday (六月 十三日 水曜日)
2007-07-14 11:24
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At Thumb mode we can use the registers is just a sub-set of those register at ARM mode. We can
use eight registers(R0~R7), PC, SP, LR and CPSR. At once at every privillege mode there are a group
of SP, LR and SPSR can be used by us. As matter of a fact, R8 ~ R12 those registers can not be used
freely. At Thumb mode, they are not standard registers there are little instructions can access them.
In CPSR, there are four conditional flags which is from 31 bit to 28 bit.
* N - Negative / Less than
* Z - Zero
* C - Carry / Borrow / Extend
* V - Overflow
At ARM mode most of instructions is runned with conditions. But at Thumb mode only those conditional
instructions used those flags.
In low 8 bits of CPSR there are four kinds of flags.
* I = 1 - disable IRQ
* F = 1 - disable FIQ
* T - it reflex the status of process.
For over version 5 and T series processes, this bit is 1, it means an application is running at
Thumb mode, otherwise, at ARM mode;
For over version 5 and non-T series processes, this bit is 1, it means next instruction will cause
a exception,
mode, otherwise, at ARM mode.
* M - M[4:0]: M0, M1, M2, M3, M4.
M[4:0] Mode Accessible Registers
10000 User PC, R14 to R0, CPSR
10001 FIQ PC, R14_fiq to R8_fiq, R7 to R0, CPSR, SPSR_fiq
10010 IRQ PC, R14_irq, R13_irq,R12 to R0, CPSR, SPSR_irq
10011 SVC PC, R14_svc, R13_svc,R12 to R0, CPSR, SPSR_svc
10111 Abort PC, R14_abt, R13_abt,R12 to R0, CPSR, SPSR_abt
11011 Undef PC, R14_und, R13_und,R12 to R0, CPSR, SPSR_und
11111 System PC, R14 to R0, CPSR (Architecture 4 only)
There are some reserved bits. They can not be used to store data.
Exception type Exception mode Vector address
Reset Supervisor 0x00000000
Undefined instructions Undefined 0x00000004
Software Interrupt (SWI) Supervisor 0x00000008
Prefetch Abort (Instruction fetch memoryabort) Abort 0x0000000c
Data Abort (Data Access memory abort) Abort 0x00000010
IRQ (Interrupt) IRQ 0x00000018
FIQ (Fast Interrupt) FIQ 0x0000001c
Address 0x14 (omitted from the above table) holds the Address Exception vector, which is only
used when the processor is configured for a 26-bit address space.
use eight registers(R0~R7), PC, SP, LR and CPSR. At once at every privillege mode there are a group
of SP, LR and SPSR can be used by us. As matter of a fact, R8 ~ R12 those registers can not be used
freely. At Thumb mode, they are not standard registers there are little instructions can access them.
In CPSR, there are four conditional flags which is from 31 bit to 28 bit.
* N - Negative / Less than
* Z - Zero
* C - Carry / Borrow / Extend
* V - Overflow
At ARM mode most of instructions is runned with conditions. But at Thumb mode only those conditional
instructions used those flags.
In low 8 bits of CPSR there are four kinds of flags.
* I = 1 - disable IRQ
* F = 1 - disable FIQ
* T - it reflex the status of process.
For over version 5 and T series processes, this bit is 1, it means an application is running at
Thumb mode, otherwise, at ARM mode;
For over version 5 and non-T series processes, this bit is 1, it means next instruction will cause
a exception,
mode, otherwise, at ARM mode.
* M - M[4:0]: M0, M1, M2, M3, M4.
M[4:0] Mode Accessible Registers
10000 User PC, R14 to R0, CPSR
10001 FIQ PC, R14_fiq to R8_fiq, R7 to R0, CPSR, SPSR_fiq
10010 IRQ PC, R14_irq, R13_irq,R12 to R0, CPSR, SPSR_irq
10011 SVC PC, R14_svc, R13_svc,R12 to R0, CPSR, SPSR_svc
10111 Abort PC, R14_abt, R13_abt,R12 to R0, CPSR, SPSR_abt
11011 Undef PC, R14_und, R13_und,R12 to R0, CPSR, SPSR_und
11111 System PC, R14 to R0, CPSR (Architecture 4 only)
There are some reserved bits. They can not be used to store data.
Exception type Exception mode Vector address
Reset Supervisor 0x00000000
Undefined instructions Undefined 0x00000004
Software Interrupt (SWI) Supervisor 0x00000008
Prefetch Abort (Instruction fetch memoryabort) Abort 0x0000000c
Data Abort (Data Access memory abort) Abort 0x00000010
IRQ (Interrupt) IRQ 0x00000018
FIQ (Fast Interrupt) FIQ 0x0000001c
Address 0x14 (omitted from the above table) holds the Address Exception vector, which is only
used when the processor is configured for a 26-bit address space.
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